Insulator



Feb. 20, 1940. H. LEE El AL INSULATOR Filed Aug. 28, 1937 1 a! 4' I 1 v m vvvvv INVENTORS v 0Z4 MHZ fiLfiAdTufl ATTORNEYS.

Patented Feb. 20, 1940 UNITED STATES INSU LATOR Lef'fman H. Lee, Bellevue, and James M. Guthrie,

Pittsburgh, Pa., assignors to Line Material Company, a corporation of Delaware Application August 28,

3 Claims.

Our invention relates to insulators for attaching electric wires to buildings and other supports.

An insulator of the sort to which the invention relates consists in a body of porcelain, glass or other suitable insulating material, and a screw for mounting the body on a support, ordinarily with the basal surface of the insulator body pressed tightly against the surface of the support. The insulator body includes a transverse bore and surface grooves that are used in making the desired attachment of an electric conductor to the mounted insulator. Such body also includes an axial bore to receive the shank of the mounting screw. In some commercial types of insulators, the head-end of the mounting screw is rigidly cemented or otherwise embedded in the body of the insulator, to form what is known as a self-mounting insulator, that may by unitary ro tation of the insulator body and screw be run home in the support. And in other types, the screws and insulator bodies are supplied separately and in making each installation an insulator body is held in the desired position on the support, while a mounting screw is inserted and screwed into the support.

In the usual insulator, the axis of the screwreceiving bore intersects at right angle the wirereceiving bore, and for this reason the head of the screw is secured in the insulator body at a point between the wire-receiving bore and the base of the body. (There must be no contact between the wire passing through the transverse bore and the mounting screw.) Thus, it is that body of the insulator, outward of the head of the mounting screw, is subjected to tension imposed by the wire threaded through the transverse bore. This is an unsatisfactory condition, the frangible body of the insulator being liable to rupture under the strain, with manifest danger and damage.

the result. For this reason, many manufacturers have provided U-shaped stirrups of metal, embracing the porcelain bodies of the insulators and reinforcing them against the stresses of service. Thus, the simple form of insulator is elaborated, with increased cost to the user.

In endeavoring to render the use of the simple two-piece (porcelain body and screw) insulator more feasible, many proposals have been advanced, but so far as we are aware none of them has entirely filled the bill. For example, it has been proposed to offset the screw-receiving bore from the true axis of the insulator body, in such manner that the screw may pass through the body from the head to the base, without intersecting the transverse wire-receiving bore in the body.

1937, Serial No. 161,406

The provision of such a structure is a step in the right direction, but certain objections are to be noted. The eccentricity of the screw-receiving bore in the insulator body requires that the insulator be accurately mounted in a particular angular position; the service load does not act on the screw centrally of the insulator body, and in some cases, not all, this is objectionable; and in the manufacture of the insulator body, particularly in the firing of porcelain, there is the matter of unequal strains to be contended with.

The object of our invention is to provide a simple two-piece insulator in which the porcelain body is uniformly reinforced by the mounting screw against the load imposed by supported wires. The insulator of our invention is easy to manufacture, inexpensive, and may be readily installed. Advantageously, the mounting screw extends centrally through the body of the insulator; the screw employed may be a screw of standard specifications, a screw of the sort now obtainable in the open market; and the screw is adapted to be assembled with the insulator body by the user, wherefore our structure is to be distinguished from the known self-mounting types of insulators, alluded to above.

In the accompanying drawing, we illustrate in exemplary way an insulator embodying the invention. Fig. I is a view in side elevation of the insulator body; Fig. II is a view in side elevation of a standard type of screw that may be employed in mounting the insulator; Fig. III is a sectional view of the insulator body, on the plane III-HI of Fig. I; Fig. IV is a view in end elevation of the insulator with the mounting screw in place; Fig. V is a view, showing the insulator mounted upon a support, the mounting screw appearing in side elevation, and the insulator body in section on the plane V-V of Fig. III; Fig. VI is a view in end elevation of the insulator, illustrating a modification in detail; and Fig. VII is a fragmentary view to larger scale of the mounting screw, illustrating in section an insulating jacket which may be applied to the head of the screw.

Referring to the drawing, the insulator comprises an integral body I of porcelain, molded to form and vitrified in usual way. The body includes a head la and a base lb,.and the crosssectional area of the base approximately equals the cross-sectional areas of the body in other transverse planes in its axial extent. The body 1 includes an axial bore 2 for the shank of a mounting screw Ill. The bore 2 is enlarged at its opposite ends; the enlargement at one end provides a seat 3 within the head of the body I,

' sulator is installed for service.

while the enlargement at the opposite end provides a recess 4 within the base of the body, providing susbtantial clearance between the shank of the screw and the wall of the bore, when the in- I As will presently appear, this clearance performs a two-fold function.

Intermediate the opposite ends of the insulator a circumferential groove 5 is formed in the body I, and in the head of the body a transverse groove 8 is formed. A pair of wire-receiving passages or bores I, 1 extend transversely through the body I; these passages open at their opposite ends in the circumferential groove 5; they are located between the seat 3, formed in the head-Ia of the body I, and the base Ib; they extend in parallelism, one on each of the opposite sides of the axial bore 2; and it is important to ends of passages 1, I open thereinto, to the transverse groove 6. The grooves 8, 8 of each pair are inclined to the axis of the body I and to each other, and mergeat their outer ends in the groove 6. As the electrician will readily perceive, the passages I, I and grooves 5. 6 and l, 8 are adapted to receive an electric conductor and tie-wires, in order to dead-end the conductor to the insulator, or to make other known attachments of the conductor to the insulator. Our structure lends itself to various known sorts of wire attachment, and the one form of insulator is serviceable where several specific forms are now required.

In mounting the insulator upon a support, say

' 'on the wooden wall a (Fig. v) of a building, the

insulator body is placed in desired position on the support, and the screw I0 is inserted in the bore 2. The screw III is screwed into the body of the support, by means of a screw driver engaged in the kerfed head IOa of the screw.

When the screw is run home and tightly secured in the support, the head of the screw bears forcefully upon the seat 3, and subjects the body of the insulator between such seat and the support to compressive stress. Thus, the porcelain body portions of the insulator, normally under tension produced by the weight of the supported wire, are held under compression. and reinforced by the head of the screw.

It will be noted that the shank of' the screw I0 is smaller than the bore 2, and this feature, together with the bore enlargement 1, provides clearance for a slight flexing of the shank of the screw, and permits substantial angular play of the insulator body upon the screw while installation is in progress, by virtue whereof the insulator adjusts itself (under the force of the driven screw) in such manner that its basal surface lb bears flat and snug upon the face of support 9. A rigid mounting of the body is thus insured.

In the insulators hitherto in common use, we have noted that the shanks of the mounting screws usually lit the bores in the insulator bodies relatively snugly, and that in consequence, when rain or other moisture enters between the base of a mounted insulator and the support, capillei-y attraction operates to draw moisture into the small clearance between the shank of the screw and the wall of the bore. This moisture remains within the bore of the insulator, tending to hasten deterioration ,of' the screw. And in cold weather the moisture trapped in the bore of the insulator freezes, expands, and bursts the porcelain body. By providing, as we do, a substantial clearance between the shank of the mounting screw and the wall of the bore, we inhibit the action of capillary attraction in drawing in moisture, and the provision of the tapering enlargement l augments the desired conditions.

In order to prevent moisture from collecting on the seat I when the insulator is mounted vertically on end, with its head directed upward, we provide a drain II, as illustrated in Fig. V. Alternately, the recess Ia in which the head Ilia of the screw lies may be filled with a plug or cement of insulating material after installation has been made.

While none of the wires passing through passages l, I and lying in grooves 5, S and 8, 8 is in contact with the mounting screw III, we contemplate enclosing the head lOa of the mounting screw in a jacket Mb (Fig. VII) of rubber or other suitable insulating material, to provide additional assurance that there shall be no grounding of the supported circuit wires.

-We have shown an ordinary wood-screw, as the means for mounting the insulator body I, but it is to be understood that in making installation on concrete or masonry walls the usual togglebolt 01'- caulked anchor-bolt may be employed. In mounting our insulator on metal supporting brackets, the usual machine screws or bolts may be employed, and we also contemplate that the mounting screws or bolts may be provided with square heads, as shown at I00 in Fig. VI, in which case the form of the socket within the head of the insulator body will be correspondingly modified. (Note the socket 3b in Fig. VI.) In

making installation with a square headed screw or bolt, the body of the insulator is rotated, and in order to facilitate the operation we fashion flat faces Ic '(Fig. I) on the side of the body I, whereby a wrench may be used with good effect.

We claim as our invention:

1. An insulator comprising a body of insulating material including a base and a head, an axial bore extending through said body, a headed mounting screw in saidbore, said bore being enlarged at its opposite ends, one enlargement forming in said body a seat for the head of said screw, an insulating jacket covering said head of the screw, a substantial clearance between the at their opposite ends with said circumferential groove, said passages being located in said body between the base thereof and the seat formed therein, whereby the head of said screw applies,

in a region outward of said wire-receiving passages, compressive stress to and reinforces said body in service, and a transverse groove formed in the head of said body, with the body being externally recessed between said transverse groove and said circumferential groove in which said transverse passages open.

2. An insulator comprising a body of insulating material including a head and a base, a circumierential groove formed in said body, a pair of wire-receiving passages extending transversely through said body and opening at their opposite ends in said circumferential groove, and the side of said head being recessed to provide wire-positioning grooves extending angularly to one another and merging to form a single groove extending transversely in the top of said head.

3. An insulator comprising a body 01' insulating material including a head and a base, a circumferential groove formed in said body, a pair of wire-receiving'passages extending transversely through said body and opening at their opposite ends in said circumferential groove, and the side of said head being recessed to provide wire-positioning grooves extending angularly to one another and merging to form a single groove extending transversely in the top of said head, and an axial bore extending through said body angularly of and between said wire-receiving passages, said axial bore being enlarged within the head of said body and providing in the body a seat 10 for the head of a mounting screw.

LEFFMAN H. LEE. JAMES M. GU'I'HRIE. 

